Dominance rank influences food hoarding in New Zealand Robins Petroica australis

Social interactions are thought to be an important determinant of food hoarding behaviour in birds. Theoretical work predicts that subordinate birds should cache more to offset losses to dominant birds. However, empirical support for this prediction is mixed. We evaluated whether social dominance influences the food hoarding behaviour of New Zealand Robins Petroica australis. Robins provide a unique opportunity to test food hoarding theory because they are fearless of humans and will cache food presented to them by hand. We offered mealworms to free-ranging male and female Robins to test whether (1) one sex was socially dominant, (2) the subordinate sex cached more frequently than the dominant sex and (3) birds cached more frequently when they were in the presence of a potential competitor. Our results indicate that males were dominant over females. Males acquired most of the prey offered to birds during trials and won all aggressive encounters observed between sexes. However, caching rates ran contrary to theoretical predictions. Males stored approximately twice as many mealworms as females. Both sexes also stored more food when they were alone than when they were accompanied by conspecifics. We interpret the reluctance of females and paired birds to hoard food as a strategy to avoid the loss of caches to competitors. Our overall results indicate that dominance rank strongly influences caching decisions, but that caching rates ran contrary to theoretical predictions.